NASA Study Finds Atmospheric Loss of Life-Protecting Ozone
WASHINGTON (AP) _ High-altitude ozone, which protects humans from skin cancer, shows an unexplained thinning of about 2.3 percent since 1969 over mid-latitudes of the Northern Hemisphere - an area that includes most of the United States, scientists said Tuesday.
The decline, which is at least twice as large in winter at high latitudes, was almost certainly the result of human use of ozone-destroying chemicals, the researchers said in what is believed to be the most definitive report on ozone concentrations to date.
Ozone, a pollutant at ground level, makes possible life on earth by blocking the harmful ultraviolet rays of the sun at high altitudes. The Environmental Protection Agency has estimated that every 1 percent decline in ozone overhead means an eventual increase in skin cancer of 5 percent to 6 percent.
Satellite data from 1978 on are consistent with a similar shrinkage in the Southern Hemisphere, according to the report of a panel assembled by the National Aeronautics and Space Administration.
The satellite data show a similar unexplained decline in ozone around the middle of the globe in both hemispheres of about 0.5 percent to 1.8 percent from 1978 to 1987. The actual decline is larger, about 2.5 percent, but most of it results from variations in the output of the sun, the panel said.
″At this point there is no other culprit to blame″ but the chlorofluorocarb on compounds, said Sherwood Rowland of the University of California, Irvine, and head of a panel subcommittee. ″We have taken out all the natural phenomena that are believed to affect ozone.″
The Senate on Monday approved, 83-0, a 31-nation treaty calling for 50 percent cuts by 1998 in production of chlorofluorocarbons, which are used for refrigeration fluids, cleaning solvents and foam blowing agents.
Since 1985, there have been several reports of ozone decline worldwide in addition to the well-established ozone ″hole″ over Antarctica - a 50 percent decline in springtime, followed by recovery.
But the reports have not been widely accepted because of such problems as out-of-calibration satellite instruments or failure to account for the solar cycle.
The NASA panel of more than 100 scientists, convened 17 months ago, went back to the original data, analyzing possible errors in observations, cross- checking ground and satellite observations and making particular use of ground data taken when a satellite was overhead.
It particular, it tried to estimate the effect of the 11-year solar cycle, which could decrease ozone by 0.7 percent to 2.0 percent in the period in question, and the effect of the two-year cycle of upper atmosphere winds.
The northern mid-latitude decline was estimated from ground-based data taken by stations mostly in the United States and Europe. There are too few stations at high latitudes, in the tropics or in the Southern Hemisphere, the panel said.
The decline reached 8 percent at the highest latitudes studied in January, averaging 6 percent in winter, and at higher northern latitudes ″limited data suggest that there has been a decrease comparable in magnitude,″ the report said.
The agency’s computer models predicted only a 4 percent to 5 percent peak decline, and researchers are asking, ″Can we believe our models?″ said Robert Watson, NASA’s chairman of the ozone panel.
Estimated average year-round ozone declines from 1969 through 1986 were reported from ground-based data for three bands in the Northern Hemisphere: latitude 30 degrees (about the latitude of Houston, Texas, Cairo and Shanghai) to 40 degrees (Philadelphia and Madrid), down 1.7 percent; 40 degrees to 53 degrees (Edmonton, Alberta, and Berlin), down 3.0 percent; and 53 degrees to 64 degrees (Fairbanks, Alaska, and Reykjavik, Iceland), down 2.3 percent.
No estimate was presented for all three bands as a whole, but Rowland said the simple mean average of the three, a 2.3 percent decline, would be close.
Each estimate contains a margin of error of about one percentage point.
The satellite data were presented similarly, with a decline of 2.5 percent before corrections for solar and other fluctuations estimated for the band between 53 degrees North and 53 degrees South (about Punta Arenas, Chile). This band covers all of the inhabited Southern Hemisphere.
The Antarctic hole is so pronounced that scientists now think of it as a year-round phenomenon because of its effects elsewhere. No one knows whether a similar ″hole″ could develop over the North Pole.
Watson said planned high-altitude research flights over the Arctic next winter will be ″absolutely essential″ in deciding whether to accelerate or change the cuts called for under the chlorofluorocarbons treaty.
Declining to make policy recommendations, Watson said, ″A fully implemented ... treaty can do absolutely nothing to remove the ozone hole over Antarctica,″ which scientists earlier had estimated could last 100 years.